1. Field of the Invention
The present invention relates to devices useful for removing objects such as thrombus/or other foreign bodies from a patient's vasculature. More particularly, the invention relates to devices useful for removing thrombus from a patient's cerebral vasculature.
2. Description of Related Art
The use of a mechanical means to restore patency to obstructed vessels is well known. These devices fit into many categories ranging from hydraulic removal of thrombus, rotating cutting blades for calcified plaque, inflatable means for crushing or dragging thrombus, or a multiplicity of metal structures that either self-expand or can be expanded to dredge a vessel or remove a stone.
Examples of these devices date back to the ‘Fogarty Catheter’ described by Fogarty in U.S. Pat. Nos. 3,367,101; 3,435,826; and 4,403,612 describing in detail improvements to a balloon catheter for embolectomy purposes. While suitable for many applications, dragging a balloon through the delicate, tortuous cerebral vasculature is not recommended. Crossing profiles of current state of the art balloon catheters would also limit their use with typical neurovascular accessories (e.g., microcatheters).
Mechanically expanded devices are also well known in the area of obstruction removal. Clark specifically focused on the use of an expanding braid for thrombus removal in U.S. Pat. No. 3,996,938. His teaching utilized a braid that would expand under the force of compression delivered by an inner core wire affixed to the distal end of the braid.
Many refinements on this theme have occurred in the areas of stone removal, clot removal, foreign body removal, etc. All of these are assemblies of some nature which either self-expand or mechanically expand under some delivered compressive load. Examples of these can be seen in Bates U.S. Pat. No. 6,800,080 in which parallel legs of the basket allow bodies to enter the retrieval basket; Bates U.S. Pat. No. 5,496,330 in which the basket is self-expanding and meant to collapse into a provided sheath; Engelson U.S. Pat. No. 6,066,158 describing a self-expanding conical basket held collapsed in a ‘delivered’ state because of a ‘fixedly attached core wire’; and Samson U.S. Pat. No. 6,066,149 describing an assembly consisting of a series of braided expanders.
These devices, while elegant, fail to address the major concern for applications into the neurovasculature; namely, minimizing the crossing profile (i.e., the cross-sectional area) of the devices. In general, these are all assembled devices consisting of many components that need to either be welded in place, or fixedly attached using collars, etc. It is not seen how a device of these inventions would be compatible with physician preferred microcatheters used to access the delicate, tortuous neurovasculature.
In many of the inventions, the issue of crossing profile has been circumvented by describing fixed wire assemblies which are not meant to pass through a microcatheter, rather, they are meant to navigate from a large guiding catheter situated well proximal of the obstruction in large vasculature. Samson U.S. Pat. No. 6,066,149 is an example of this type of assembly. As demonstrated in the figures, the device is an assembly in which the wire ends are managed into a collar. The retractable core wire doubles as a conventional guidewire tip at its distal termination. This tip affords the steering of a guidewire and the ability to puncture a clot to cross it, while the large body of the device encompasses the expander. Perhaps suitable for easily accessible obstructions, this does not address the majority of anticipated cerebral vascular cases, or the physician preference, where a microcatheter/guidewire combination is used to create a pathway across the clot for angiographic visualization distal to the clot prior to the procedure.
Wensel has anticipated the need for smaller devices to achieve neurovasculature compatibility in U.S. Pat. No. 5,895,398. In this publication, he teaches the use of a helically shaped wire held straight for delivery by the microcatheter. By using a single wire shaped into a ‘cork-screw’ he has circumvented the complex assembly steps required in much of the other prior art resulting in large profiles. His invention, unfortunately, places the need of restraint on the microcatheter. Typically, physician preferred microcatheters are extremely flexible at the distal end lending little ability to hold a shaped wire straight. This results in a trade-off of making the ‘cork-screw’ floppy (which degrades its ability to extract a clot), or making a custom microcatheter which is stiff, limiting procedural access. Wensel's teaching also results in a structure which is not optimized for preventing the distal migration of particulate during the removal of clot due to the inherently large intertices of a device comprised of only a single, helically shaped wire.